Java Hacks and Tricks for Prograramming

Here are the few java tricks and codes which will definitely help you to improve your programming skills.

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import java.math.BigInteger;

import java.util.*;

public class Document {

public static void main(String args[]) {

Scanner in = new Scanner(System.in);

String str = "Adarsh";

//replace substring in a String

String result = str.replaceFirst("ar", "A");

System.out.println(result);

//String upper case

System.out.println("String upperCase: " + str.toUpperCase());

//String lower case

System.out.println("String lowerCase: " + str.toLowerCase());

//length of string

System.out.println("Length: " + str.length());

//first index in string

System.out.println("First index of 'r': " + str.indexOf('r'));

//last index in string

System.out.println("Last index of 'a': " + str.lastIndexOf('a'));

//String difference

System.out.println("compare with 'Kumar': " + str.compareTo("Kumar"));

//String contains char sequence

System.out.println(str+" contain 'arsh': "+str.contains("arsh"));

//String to char Array

char charArray[] = str.toCharArray();

System.out.print("Char Array: ");

System.out.println(charArray);

//List to Array

List<String> list = Arrays.asList("C", "C++", "Java");

String[] array = list.toArray(new String[list.size()]);

System.out.println(Arrays.toString(array));

//ASCII

System.out.println("ASCII of numbers");

for(int i=48; i<57; i++){

System.out.print((char)i);

}

System.out.println();

System.out.println("ASCII of A-Z");

for(int i=65; i<91; i++){

System.out.print((char)i);

}

System.out.println();

System.out.println("ASCII of a-z");

for(int i=97; i<123; i++){

System.out.print((char)i);

}

System.out.println();

//character Input

System.out.println("Enter a Character");

char ch = in.next().charAt(0);

//Subtring

System.out.println("Substring of "+str+" 0 to 4 is: "+str.substring(1,4));

//String to Integer

String num = "100";

System.out.println("Integer form of '100': "+Integer.parseInt(num));

//Swapping of 2 numbers using XOR:

int a = 4, b=5;

System.out.println("Before Swapping a="+a+", b="+b);

a ^= b;

b ^= a;

a ^= b;

System.out.println("After Swapping a="+a+", b="+b);

//Multiply by 2

System.out.println("Multiply 3 with 2: "+ (3 << 1));

//Divide by 2

System.out.println("Divide 6 with 2: "+ (6 >> 1));

//Number of Digit

System.out.println((int)Math.floor(Math.log10(556)) +1);

//GCD using BigInteger

BigInteger b1 = BigInteger.valueOf(10);

BigInteger b2 = BigInteger.valueOf(5);

System.out.println("GCD of 10 & 5: "+b1.gcd(b2));

//Check Prime Number

System.out.println("Is 9 prime?: "+BigInteger.valueOf(9).isProbablePrime(1));

//Check if number is power of 2 or not

int x = 7;

System.out.println("Is "+x+" power of 2? "+(x!=0 && ((x&(x-1)) == 0)));

//sort array

int numArray[] = {1, 5, 3, 2, 4};

Arrays.sort(numArray);

for(Integer n: numArray){

System.out.print(n + " ");

}

System.out.println();

char ch2 = 'a';

//upper case character

ch2 = Character.toUpperCase(ch2);

System.out.println("Character upper case: "+ch2);

//lower case character

ch2 = Character.toLowerCase(ch2);

System.out.println("Lower upper case: "+ch2);

//List Sorting

List<Integer> numList= new ArrayList<>();

numList.add(5);

numList.add(1);

numList.add(3);

System.out.println("List Before Sorting");

for(Integer n: numList){

System.out.print(n+" ");

}

System.out.println();

Collections.sort(numList);

System.out.println("List After Sorting");

for(Integer n: numList){

System.out.print(n+" ");

}

System.out.println();

//Hash Map

HashMap<String, Integer> numHash = new HashMap<>();

numHash.put("A",65);

numHash.put("B",66);

numHash.put("C",67);

if(numHash.containsKey("A"))

System.out.println(numHash.get("A"));

if(numHash.containsValue(66))

System.out.println(numHash.get("B"));

System.out.println("Size Of HashMap: "+numHash.size());

numHash.remove("A");

System.out.println("Size Of HashMap after removing First Object: "+numHash.size());

numHash.replace("C",0);

System.out.println(numHash.get("C"));

numHash.clear();

if(numHash.isEmpty())

System.out.println("HashMap is Empty");

//Stack

Stack<Integer> stack = new Stack<>();

stack.push(2);

stack.push(3);

stack.push(4);

System.out.println("Top Element in Stack: "+stack.peek());

System.out.println("Popping Top Element in Stack: "+stack.pop());

System.out.println("Top Element in Stack: "+stack.peek());

stack.clear();

if (stack.isEmpty())

System.out.println("Stack is Empty");

}

Output

AdAsh

String upperCase: ADARSH

String lowerCase: adarsh

Length: 6

First index of 'r': 3

Last index of 'a': 2

compare with 'Kumar': -10

Adarsh contain 'arsh': true

Char Array: Adarsh

[C, C++, Java]

ASCII of numbers

012345678

ASCII of A-Z

ABCDEFGHIJKLMNOPQRSTUVWXYZ

ASCII of a-z

abcdefghijklmnopqrstuvwxyz

Enter a Character

Substring of Adarsh 0 to 4 is: dar

Integer form of '100': 100

Before Swapping a=4, b=5

After Swapping a=5, b=4

Multiply 3 with 2: 6

Divide 6 with 2: 3

GCD of 10 & 5: 5

Is 9 prime?: false

Is 7 power of 2? false

1 2 3 4 5

Character upper case: A

Lower upper case: a

List Before Sorting

5 1 3

List After Sorting

1 3 5

Size Of HashMap: 3

Size Of HashMap after removing First Object: 2

HashMap is Empty

Top Element in Stack: 4

Popping Top Element in Stack: 4

Top Element in Stack: 3

Stack is Empty